An on-board charger (OBC) of an electric vehicle is used for charging a traction battery of the vehicle. The OBC charges the traction battery using AC electrical power from a mains supply. The OBC has an input which is connected to the mains supply by an external Electric Vehicle Supply Equipment (EVSE) to receive AC electrical power from the mains supply. The OBC converts AC electrical power received from the mains supply into DC electrical power. The OBC has an output which connects to the traction battery. The OBC provides DC electrical power, converted from the AC electrical power, to the traction battery for charging the traction battery.
Most OBCs have two cascaded stages with a DC link capacitor connected between the stages. The first stage is generally known as a Power Factor Correction (PFC) stage and the second stage is generally known as a DC/DC stage. The PFC stage drains AC electrical power from the mains supply and is responsible for keeping a power factor (PF) close to unity. The PFC stage converts AC electrical power from the mains supply into DC electrical power and delivers this DC electrical power to the DC link capacitor and to the DC/DC stage. The DC/DC stage is responsible for delivering DC electrical power to the output of the OBC through a DC/DC converter. The traction battery is connected to the output of the OBC. In steady-state operation (e.g., a stable operation mode) of the OBC, the voltage of the DC link capacitor is boosted and regulated at a certain DC voltage level; and the traction battery is charged with DC electrical power from the DC link capacitor via the DC/DC converter.
Before charging the traction battery, the DC link capacitor is to be pre-charged to avoid a surge electrical current from the mains supply when the OBC has just been connected to the mains supply. Such surge electrical currents could damage internal components of the OBC and/or could be transferred back to the mains supply and damage the mains supply. Typically, in a pre-charge operation mode of the OBC, the DC link capacitor is charged from a low voltage to a peak voltage of the mains supply. Once the DC link capacitor is charged to a sufficient level (e.g., the peak voltage of the mains supply), the PFC stage of the OBC starts regulating the DC link capacitor voltage to the desired voltage to move the OBC into the stable operation mode.